1. Field of the Invention
This specification relates to a bistable permanent magnetic actuator, and more particularly, an actuator for working a circuit breaker and a switch of electric power equipment using a magnetic force of a permanent magnet.
2. Background of the Invention
In regard of a low voltage circuit breaker of about several hundred volts, and a high voltage circuit breaker of several kilovolts or more or a super high voltage circuit breaker of several hundred kilovolts or more, widely used types of actuators for providing a driving force to switch on or off (open or close) contact points generally include a spring type, which uses elastic energy accumulated in a spring to obtain a switching driving force, and a hydro-pneumatic type, which uses hydraulic pressure and air pressure to obtain the switching driving force.
However, the spring type actuator has the structure of providing the switching driving force by cooperation with many mechanical components, which may be difficult to acquire operation reliability. Furthermore, the hydro-pneumatic type actuator provides a switching driving force sensitive to the change in temperature, which may also be difficult to acquire the operation reliability.
To overcome such problems, in recent time, a so-called permanent magnetic actuator using a permanent magnet and electric energy is being used instead of the existing actuators. The permanent magnetic actuator is configured to secure (fix) a movable element therein to be movable within a predetermined stroke using the magnetic force of the permanent magnet and make the movable element moved within the stroke by interaction of a magnetic force generated by supplying electric energy to a coil. In response to the movement of the movable element, a circuit breaker is opened or closed.
The permanent magnetic actuators may be classified into a bistable type and a monostable type according to the type of movable element (member) being secured at a certain position. The bistable type has a structure that the movable element is fixed by the permanent magnet at both ends of a certain stroke, and the monostable type has a structure that the movable element is fixed at one of both ends of the stroke.
Among the two types, the bistable permanent magnetic actuator is more advantageous than the monostable type requiring a separate suspending member, in the aspect that the movable element is fixed by the magnetic force of the permanent magnet so as to allow a closing/opening operation without a separate member in both cases of performing opening and closing operations with respect to electric power equipment, namely, bidirectionally moving the movable element.
FIG. 1 is a sectional view showing an embodiment of a bistable permanent magnetic actuator. As shown in FIG. 1, the actuator includes an upper cylinder 14 having an upper coil 12 wound therein, a middle cylinder 18 located at a lower side of the upper cylinder 14 and fixing a permanent magnet 16, and a lower cylinder 22 having a lower coil 20 wound therein. The upper, middle and lower cylinders are assembled to define a hollow hole, in which a movable element 24 is installed to be movable up and down. An open spring 26 is installed at one end of the movable element 24.
Referring to FIG. 1, the movable element 24 remains secured by the magnetic force of the permanent magnet 16 in a contact state with a protruded portion of the lower cylinder 22. Under this state, when a current is applied to the upper coil 12, as shown in FIG. 2, the upper cylinder 14 is magnetized to apply an upward force to the movable element 24. Once the force becomes stronger than the magnetic force of the permanent magnet 16, the movable element 24 is moved up to be in a state shown in FIG. 3.
In this state, the movable element 24 remains in the state shown in FIG. 3 by virtue of the magnetic force of the permanent magnet 16 even if the current is blocked. Afterwards, when a current is applied to the lower coil 20, the lower cylinder 22 is magnetized and thereby the movable element 24 is moved down to be back into the state shown in FIG. 1. As such, the movable element can be reciprocated up and down by applying the current to the upper and lower coils, respectively, and the reciprocating motion of the movable element allows the circuit breaker to be tripped/closed.
Here, the open spring 26 is compressed when the movable element 24 is located at a lower side, and decompressed when the movable element 24 is located at an upper side. Also, the open spring 26 is provided to more facilitate performing of an opening operation when a contact point is manually opened from external electric power equipment in a state that the permanent magnetic actuator is connected to the electric power equipment (circuit breaker or switch).
The related art permanent magnetic actuator having the structure has a merit in that such structure is simpler than other existing actuators and operates stably even without separate repair and maintenance. However, as shown in the drawings, each of the upper, middle and lower cylinders should be fabricated through a mechanical work, which requires a high machining cost. Also, such cylinders should be precisely assembled to ensure a smooth operation of the movable element. However, the precise assembly is difficult.
In addition, the permanent magnet should be processed into an annular shape, the processing cost for the magnet is also increased. Use of a single permanent magnet makes the assembly difficult due to the strong magnetic force of the permanent magnet. In view of the structure, the permanent magnet and the movable element are in a contact state, which may cause damages on the permanent magnet due to collision between the permanent magnet and the movable element during operation of the movable element.